1. Field of the Invention
This invention relates to an activator for cyanoacrylate adhesives based on N,N-dialkyl aniline derivatives, to its production and use and to the combination product of the activator and the cyanoacrylate adhesive.
An "activator" is generally understood to be an accelerator used separately to cure a chemically reacting one-component adhesive. In the present case, the polymerization of 2-cyanoacrylates in particular is activated.
2. Description of Related Art
Activators as defined above are known. Thus, DE-OS 24 13 406 describes particles of a porous support impregnated with an N,N-dialkyl-substituted aniline containing 1 to 4 carbon atoms in the alkyl radical for initiating the delayed polymerization of monomeric cyanoacrylates. The delay is brought about by the porous supports. The N,N-dialkyl-substituted anilines used include N,N-dimethyl aniline, N,N,2,4-tetramethyl aniline, N,N,3,5-tetramethyl aniline, N,N-dimethyl-o-toluidine, N,N-dimethyl-m-toluidine, N,N-dimethyl-p-toluidine, N-methyl-N-phenylbenzyl amine and/or their corresponding N-ethyl and N,N-diethyl derivatives.
N,N-Dimethyl-p-toluidine is preferred. The adhesive bonds obtained are not transparent. The invention is intended for the field of dental medicine. The disadvantage that N,N-dimethyl toluidine is toxic and has an unpleasant odor is particularly serious in this case.
Accordingly, there has been no shortage of attempts to use less toxic activators. In Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 19(2), pages 585-90, aniline derivatives were investigated both from this viewpoint and for cure time, strength and color stability. Besides N,N-dimethyl toluidine and xylidine, 4-N,N-dimethylaminobenzaldehyde and benzoic acid and methyl esters thereof were among the aniline derivatives investigated. Although these compounds may be less toxic, they are still unsuitable for use as activators because they activate far too weakly, if at all. Other activators rapidly form a skin with subsequent slow curing when solutions thereof are sprayed onto a monomeric cyanoacrylate layer. The shock-like curing at the surface results in a wrinkled structure which, in addition, destroys transparency in most cases.
Accordingly, N,N-dimethyl toluidine remains the only effective activator for cyanoacrylates. Since it is classified as a "T substance" under the legislation on chemicals, this activator has to be used in a concentration of more than 1%. Further disadvantages of the known activator are its volatility, which releases DMT even after bonding, and the unpleasant odor associated therewith.
Accordingly, the problem addressed by the present invention was to remedy this situation by providing an activator which would have few, if any, of these disadvantages and which would be better in its handling and performance properties than known activators, particularly in regard to the balance between transparency, odor, toxicity, curing behavior, strength and surface structure.